In processes for producing semiconductor thin film devices, optical devices, super steel materials and the like, there have been produced various thin films, thick films and the like by means of CVD method, sputtering method, sol-gel method, vapor deposition method and the like. Moreover, in order to form a circuit pattern, gas etching for partially removing a thin film material has been conducted on semiconductors or in fabrication of semiconductors for IC, LSI, TFT and the like.
Hitherto, perfluorocarbons (PFCs) such as CF4, C2F6, C3F8 and the like have been used as an etching gas in etching for forming circuits, in fabrication of thin film devices. However, these gases exist in the environment stably for a long period of time and therefore regarded as having high global warming potentials, so that their adverse influence on the environment has come to an issue.
For example, their GWPs known from the IPCC Fourth Assessment Report are as follows (on a 100 year scale):
CF4: 7390
C2F6: 12200
C3F8: 8830
An etching gas partially having the structure of CF3 group e.g. C2F6, C3F8 and the like generates active species exemplified by CF3 radicals, ions and the like in a deposition room (a chamber) thereby exhibiting the etching effect; however, CF3 active species are brought into contact with fluorine radicals or with fluorine active species of ions to be recombined thereto, thereby forming CF4 as a by-product.
Guidelines on the destruction of PFCs issued by Office of Fluorocarbons Control Policy, Global Environmental Issues Division of the Global Environment Bureau of the Ministry of the Environment (issued in March 2009) states that CF4 is the most undecomposable PFC in the environment and therefore it may not be sufficiently destructed under the destructing conditions similar to those for other fluorocarbons.
As a fluorine-containing etching gas having low global warming potentials and substitutable for PFC, there have been proposed COF2, CHF2OF (Patent Publication 1), CF3COF (Patent Publications 2 and 3) and the like. These publications state it is possible to reduce by-production of CF4, for example, by optimizing an etching condition for CF3COF.